1. Field of the Invention
The present invention relates to a car antitheft apparatus for preventing driving of a car when the car has been stolen.
2. Description of the Prior Art
When a car is stolen, the illegal operation of a starter circuit (direct connection of a starter power supply), use of a forged key and the like are conceivable, and countermeasures against these are required.
An antitheft apparatus for preventing these is disclosed by, for example, Japanese Laid-open Patent Application No. 6-227364. In this antitheft apparatus, paying attention to a recent increase in the number of cars in which the amount of fuel to an engine and the ignition time are controlled by an engine controller, it is electronically judged whether the key used to start the engine is a correct key, data on whether the engine should be started is electronically transmitted to the engine controller based on the result of this judgment, and the supply of fuel to the engine and ignition are controlled to start the engine. Stated more specifically, this antitheft apparatus collates an electronic code stored in the key with the preset correct code and outputs the result of collation to the engine controller which in turn judges whether the engine should be started according to the result of collation received from the above antitheft apparatus and does not control the engine until it judges that the engine can be started.
However, information on whether the engine should be started with a correct key is transmitted and received over a single communication line, and the start of the engine is delayed by a time required for the transmission and reception of the above information when the supply of fuel to the engine and ignition are controlled.
According to the operational environment at the time of the start of the engine (when the temperature is extremely low or a weak battery is used), it is difficult to ensure an operation voltage for the communication line for exchanging the above information, thereby making it difficult to transmit and receive correct information and further extending the time required for the transmission and reception of the information. As a result, there is a possibility that the startability of the engine further deteriorates.
Since there are differences in reset/reset canceling voltage and reset canceling timing between the antitheft apparatus and the engine controller, there is a difference in information exchange start timing between these apparatuses. As a result, it is possible that there occurs a so-called communication collision that the transmission and reception of information on whether the engine should be started cannot be performed smoothly due to a difference in recognition between the apparatuses, the time required for the transmission and reception of the information is extended, and the startability of the engine further deteriorates.
The applicant of the present invention proposes a technology for preventing a delay in the start of the engine by eliminating the above communication collision by providing a communication protocol for returning the result of recognizing the contents of transmission data on a receiver's side when data is transmitted from either the antitheft apparatus or the engine controller.
However, since the start of the engine is impossible during a time required for the communication of information for judging whether the engine should be started in all of the above prior arts, even when the engine is started with a correct key, the engine cannot be started immediately after the key switch is turned on.